Data recorder

ABSTRACT

A data recorder for recording data that prevents buffer overrun errors emits a laser beam against a recording medium to record data. The data has a level that determines the power of the laser beam. When there is a possibility of a buffer overrun, data recording is interrupted. The interruption is carried out when the power of the laser beam is a low level. Data recording is restarted with the laser beam generated at the low level.

BACKGROUND OF THE INVENTION

The present invention relates to a data recorder, and more particularly,to a data recorder having a buffer memory for storing data provided froman external device and recording the stored data of the buffer memory ona recording medium.

An optical disc recorder records data on an optical disc, which servesas a recording medium. A CD-DA family compact disc-recordable (CD-R)drive is one type of optical disc recorder that is widely used. A CD-Ris a so-called write-once optical disc on which data is written onlyonce. The recorded data cannot be physically deleted. A laser beam isirradiated against the optical disc from an optical head of the CD-Rdrive. The heat of the laser beam melts a dye and forms recording pitson a recording layer of the optical disc. Data is recorded on the discby changing the reflecting rate of the recording layer.

The optical disc recorder includes a buffer memory and an encoder. Thebuffer memory temporarily stores data provided from an external device,such as a personal computer. The encoder reads the data from the buffermemory and encodes the read data to record the data on the optical disc.

In such an optical disc recorder, if, for example, the rate of datatransmission from the external device is slower than the recording datatransmission rate of the optical disc (write speed), the transmissionrate of the recording data output from the encoder is faster than thetransmission rate of the data provided to the buffer. This decreases theamount of data stored in the buffer memory. If the decrease continues,the data amount ultimately becomes null and the buffer memory becomesempty. This stops the stream of data to the encoder and causes aninterruption in the data recorded on the optical disc. This problem isreferred to as buffer underrun. The interruption in the data recorded onthe optical disc resulting from buffer underrun is referred to as abuffer underrun error.

Data is recorded on an optical disc using a recording technique thatdesignates the file group recorded on the optical disc (e.g., disc atonce, track at once). Thus, if a buffer underrun error occurs, theentire optical disc becomes unusable when employing disc at once, andthe track undergoing recording becomes unusable when employing track atonce.

Recent CD-R drives record data at a speed four times or eight times thenormal recording speed. Further, recent personal computers havemultitasking functions to operate CD-R drives. This has increased thetendency of the occurrence of buffer underrun errors.

Packet writing is one type of data recording that records data in packetunits. Packet writing records data on an optical disc when the datareaches the capacity of the packet. This prevents the occurrence ofbuffer underrun errors. However, link blocks must be formed to connectpackets in packet writing. The link blocks decrease the recordingcapacity of the optical disc. Further, there are CD-ROM drives that arenot capable of handling packet writing. Such CD-ROM drives cannotreproduce data written to optical discs through packet writing. In otherwords, the CD-ROM compatibility required by the CD-R standard (OrangeBook Part II) does not include packet writing. For example, packetwriting cannot be applied for a CD-DA player. Thus, a CD-R drive cannotrecord CD-DA audio data through packet writing. Accordingly, there is aneed for preventing buffer underrun errors without employing packetwriting.

A CD-rewritable (CD-RW) drive is another type of optical disc recorderthat is widely used. A CD-RW drive irradiates a laser beam from anoptical head against an optical disc. The heat of the laser beam causesphase changes between amorphic and crystalline to form recording pits onthe recording layer of the optical disc. This changes the reflectingrate of the recording layer and records data on the optical disc. Datacan be repeatedly rewritten to optical discs used by the CD-RW drive.Accordingly, the optical disc remains usable even if a buffer underrunerror occurs. However, when a buffer underrun error occurs, the datafile that was being recorded before the occurrence of the bufferunderrun error must be recorded again. This wastes the recordingperformed prior to the occurrence of the buffer underrun error andincreases the recording time.

A magneto-optic disc recorder is another type of known data recorder.The magneto-optic disc recorder irradiates a laser beam from an opticalhead against a magneto-optic disc. This applies residual magnetizationto the recording layer of the optical disc and records data on themagneto-optic disc. Mini disc (MD) drives are widely used magneto-opticdisc recorders. However, MD drives have the same problem as CD-RWdrives.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a data recorder thatrecords data in a manner that the continuity of the data is ensured evenif the recording of data to a recording medium is interrupted.

To achieve the above object, the present invention provides a datarecorder for recording data on a recording medium by emitting a laserbeam against the recording medium. The data recorder includes aninterrupt control circuit for interrupting data recording when apredetermined state is detected. The interruption occurs when the laserbeam is generated at a relatively low power level.

A further aspect of the present invention provides a data recorder forrecording data on a recording medium by emitting a laser beam againstthe recording medium. The data recorder includes a buffer memory fortemporarily storing data that is to be recorded on the recording medium,an interrupt control circuit for interrupting data recording when apredetermined state is detected, and an address memory connected to thebuffer memory. The address memory stores at least one of an address ofthe recording medium and an address of the buffer memory when datarecording on the recording medium is interrupted. Each address indicatesa location of data when the recording interruption occurred. Asynchronizing circuit sequentially reads the data recorded on therecording medium prior to the recording interruption and the data storedin the buffer memory prior to the recording interruption whilesynchronizing the recorded data and the stored data. A restart circuitrestarts data recording on the recording medium based on the addressstored in the address memory. The interrupt control circuit interruptsdata recording when the laser beam is generated at a relatively lowpower level.

Another aspect of the present invention provides a data recorder forrecording data on a recording medium by emitting a laser beam againstthe recording medium. The data is formed by a plurality of sectors. Eachof the sectors includes a synch pattern that has a predetermined numberof bits representing a low level. The laser beam is generated at a lowpower level in accordance with the low level of the synch pattern. Thedata recorder includes an interrupt control circuit for continuingrecording until an interval between sectors appears when detecting apredetermined state and interrupting the recording operation when thelaser beam is generated in accordance with the synch pattern of asector.

A further aspect of the present invention provides a data recorder forrecording data on a recording medium. The recorder includes a buffermemory for temporarily storing data, an encoder connected to the buffermemory to encode the data read from the buffer memory and to generaterecording data, and a recording unit connected to the encoder to emit alaser beam against the recording medium in accordance with the recordingdata and record the recording data on the recording medium. An interruptcontrol circuit is connected to the encoder to detect a predeterminedstate during data recording. Upon the detection of the predeterminedstate, the interrupt control circuit controls the encoder so that datarecording is interrupted when the laser beam is generated at arelatively low power level.

Another aspect of the present invention provides a method for recordingdata on a recording medium by emitting a laser beam against therecording medium. The data is formed by a plurality of sectors. Each ofthe sectors includes a synch pattern that has a predetermined number ofbits representing a low level. The laser beam is generated at a lowpower level in accordance with the low level of the synch pattern. Themethod includes continuing recording until an interval between sectorsappears when a predetermined state is detected, and interrupting therecording operation when the laser beam is generated in accordance withthe synch pattern of a sector.

A further aspect of the present invention provides a method forrecording data on a recording medium by emitting a laser beam againstthe recording medium. The method includes temporarily storing data in abuffer memory, recording data read from the buffer memory on therecording medium, interrupting data recording when a predetermined stateis detected, and storing in an address memory at least one of an addressof the recording medium and an address of the buffer memory when datarecording on the recording medium is interrupted. Each address indicatesa location of data when the recording interruption occurred. The methodfurther includes sequentially reading the data recorded on the recordingmedium prior to the recording interruption and the data stored in thebuffer memory prior to the recording interruption, synchronizing therecorded data and the stored data, and restarting data recording on therecording medium based on the address stored in the address memory. Theinterrupting of the data recording is performed when the laser beam isgenerated at a relatively low power level.

Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing a CD-R drive according to apreferred embodiment of the present invention;

FIG. 2( a) is a schematic diagram showing a sector of an optical disc;and

FIG. 2( b) is a diagram illustrating addresses of a buffer memory of theCD-R drive of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a CD-R drive 1 includes a spindle motor 2, aspindle servo circuit 3, an optical head 4, an RF amplifier 5, a headservo circuit 6, a decoder 7, a subcode decoding circuit 8, a wobbledecoder 9, an ATIP decoding circuit 10, an external connection terminal11, an interface 12, a buffer memory 13, an encoder 14, an encoderinternal RAM 15, a laser drive circuit 16, a crystal oscillation circuit18, an access control circuit 19, a buffer underrun determinationcircuit 20, a recording control circuit 21, and a system control circuit22. The CD-R drive 1 is connected to a personal computer 31 via theexternal connection terminal 11 to record data, which is provided fromthe personal computer 31, on an optical disc 32 that complies with theCD-R standards. Further, the CD-R drive 1 provides the personal computer31 with data reproduced from the optical disc 32.

The spindle motor 2 rotates the optical disc 32. The spindle servocontrol circuit 3 controls the spindle motor 2 so that the optical disc32 is rotated using the constant linear velocity (CLV) method inaccordance with the rotation control signal generated by the wobbledecoder 9.

When reading data, the optical head 4 irradiates a relatively weak laserbeam against the optical disc and, from the reflected laser beam,generates a RF signal (high frequency signal) in correspondence with thedata recorded on the optical disc. When recording data, the optical head4 irradiates a relatively intense laser beam (several tens of timesgreater than the data reading laser beam) against the optical beam 32 toform recording pits on the recording layer of the optical disc 32 andchange the reflecting rate of the recording layer to record data. Insynchronism with the recording of data, the optical head 4 generates theRF signal in correspondence with the recorded data from the reflectedlaser beam.

The RF amplifier 5 amplifies the RF signal, which is provided from theoptical head 4, and digitizes the amplified RF signal to generate adigital data signal. The RF signal of the optical head 4 is fed back tothe head servo circuit 6 via the RF amplifier 5. The head servo circuit6 uses the RF signal to perform focusing control, tracking control, andsled feed control. Focusing control focuses the laser beam on therecording layer of the optical disc 32. Tracking control tracks thelaser beam along a signal track of the optical disc 32. Sled feedcontrol moves the optical head 4 in the radial direction of the opticaldisc 32.

The decoder 7 decodes the digital data provided from the RF amplifier 5.Further, the decoder 7 generates a pit clock from the digital data andseparates a subcode from the digital data to generate a subcodesynchronizing signal.

The subcode decoding circuit 8, which is incorporated in the decoder 7,decodes the subcode. Further, the subcode decoding circuit 8 generatessubcode Q channel data (hereafter referred to as sub-Q data) from thedecoded subcode.

The wobble decoder 9 extracts a wobble component of 22.05 kHz from apre-groove signal of the optical disc 32 that is included in the digitaldata provided from the RF amplifier 5. Then, the wobble decodergenerates the rotation control signal of the optical disc 32 from thewobble component.

The ATIP decoding circuit 10, which is incorporated in the wobbledecoder 9, uses the wobble component to decode an absolute time inpre-groove (ATIP) and extract absolute time information, or an ATIPaddress, from the ATIP. The absolute time information indicatesaddresses of locations in the recording medium.

The interface 12 controls data transmission between the personalcomputer 31 and the CD-R drive 1.

The buffer memory 13 is a ring buffer that includes a synchronousdynamic random access memory (SDRAM), which preferably has a FIFOconfiguration, and the buffer memory 13 stores data provided from thepersonal computer 31 via the interface 12. Data stored at one address ofthe buffer memory 13 corresponds to data recorded at one sector of theoptical disc 32.

An interrupt/restart circuit 43 of the system control circuit 22controls the encoder 14. The encoder 14 reads the data stored in thebuffer memory 13 in sector units and encodes the data into recordingdata for the optical disc 32. The RAM 15, which is incorporated in theencoder 14, stores the necessary data for encoding by the encoder 14 andintermediate operation encoding data. When performing data encoding incompliance with the CD-ROM standard, the encoder 14 adds a synch byte, aheader, CD-ROM data error detection code (EDC), and an error correctioncode (ECC) to the data. The encoder 14 further performs error correctionusing a cross interleaved Reed-Solomon code (CIRC), which is a CD errorcorrection code, and eight to fourteen modulation (EFM) on the data.Further, the encoder 14 adds a subcode, which includes the sub-Q data,and a synchronizing signal of the subcode to the data.

The interrupt/restart circuit 43 also controls the laser drive circuit16, which provides a laser drive signal to the laser beam source of theoptical head 4. The voltage of the drive signal is constant whenreproducing data and varied in accordance with the recording data outputfrom the encoder 14 when recording data. When the recording data outputfrom the encoder 14 is low (L), recording pits are not formed on therecording layer of the optical disc 32. Thus, the drive signal is set sothat its voltage is the same as when data is reproduced. When therecording data is high (H), recording pits are formed on the recordinglayer of the optical disc 32. Thus, although the voltage of the drivesignal differs between track positions, the drive signal is set so thatits voltage is several tens of times greater than during datareproduction.

The crystal oscillation circuit 18 generates an oscillation signal basedon the oscillation of a crystal oscillator.

The access control circuit 19 selectively refers to the subcode addressof the absolute time information in the sub-Q data and the ATIP addressof the absolute time information in the ATIP to control the recordingcontrol circuit 21 and the head servo circuit 6. This controls access tothe optical disc 32.

The data provided to the buffer memory 13 is stored in the buffer memory13 in a predetermined address order. The buffer underrun determinationcircuit 20 directly or indirectly determines the amount of data storedin the buffer memory 13 from the address at which writing or reading ispresently performed. Based on the data amount, the buffer underrundetermination circuit 20 determines whether or not the buffer memory 13is in a state in which buffer underrun may occur.

Based on the determination result of the buffer underrun determinationcircuit 20 and in response to a command provided from the personalcomputer 31, the recording control circuit 21 controls the interface 12,the access control circuit 19, and the system control circuit 22.

The system control circuit 22 includes a system clock generation circuit41, a signal synchronizing circuit 42, the interrupt/restart circuit 43,a retry determination circuit 44, location detection circuits 45, 46,and address memories 47, 48. These circuits 41–48 are laid out on thesame chip of an LSI substrate.

The system clock generation circuit 41 generates from the oscillationsignal of the crystal oscillation circuit 18 a reference clock used whenrecording data. Further, the generation circuit 41 uses a pit clockextracted by the decoder 7 to generate a reproduction clock used whenreproducing data. The generation circuit 41 selects the reference clockor the reproduction clock in accordance with the switching controlperformed by the signal synchronizing circuit 42. The selected clock isused as a system operational clock of the CD-R drive 1. In accordancewith the operational clock, the CD-R drive 1 controls thesynchronization of the circuits 7–10, 12–16, and 19–22.

In accordance with the synchronizing signal of the subcode from thedecoder 7 and the sub-Q data from the subcode decoding circuit 8, thesignal synchronizing circuit 42 controls the recording control circuit21 so that the recording data output from the encoder 14 is synchronizedwith the data recorded on the optical disc 32. When performing thiscontrol, the sub-Q data of the subcode decoding circuit 8 is associatedwith the sub-Q data of the encoder 14 after synchronizing the subcodesynchronizing signal of the decoder 7 with the subcode synchronizingsignal of the encoder 14. The signal synchronizing circuit 42 controlsthe system clock generation circuit 41 so that the reference clock orthe reproduction clock is output.

The recording control circuit 21 controls the interrupt/restart circuit43. The interrupt/restart control circuit 43 controls the encoder 14 andthe laser drive circuit 16 and, when the buffer underrun determinationcircuit determines that the buffer memory 13 has entered a state inwhich buffer underrun may occur, provides the address memories 47, 48with a recording interrupt signal.

The address memory 47 stores the address of the read data in the buffermemory 13 when receiving the recording interrupt signal from theinterrupt/restart circuit 43.

The address memory 48 stores the address of the ATIP decoded by the ATIPdecoding circuit 10 when receiving the recording interrupt signal fromthe interrupt/restart circuit 43.

When data is reproduced during a recording restart mode (describedlater), the location detection circuit 45 compares the address of thedata read from the buffer memory 13 with the address stored in theaddress memory 47. If the data address and the stored address are thesame, the location detection circuit 45 activates the recording restartsignal.

When data is reproduced during the recording restart mode, the locationdetection circuit 46 compares the address of the ATIP decoded by theATIP decoding circuit 10 with the ATIP address stored in the addressmemory 48. If the decoded ATIP address and the stored ATIP address arethe same, the location detection circuit 46 activates the recordingrestart signal.

The retry determination circuit 44 instructs the recording controlcircuit 21 to restart the recording operation of the interface 12, theaccess control circuit 19, and the system control circuit 22 when therestart signals of the location detection circuits 45, 46 aresimultaneously activated. When the two restart signals are notsynchronously activated (when the restart signals are activated atdifferent timings), the retry determination circuit 44 instructs thecontrol circuit 21 to repeatedly perform data reproduction in therecording restart mode until the two restart signals are synchronouslyactivated.

The operation of the CD-R drive 1 will now be discussed.

When a user manipulates the personal computer 31 to record data, thepersonal computer 31 generates a command accordingly. The command istransferred to the recording control circuit 21 via the interface 12. Inresponse to the command, the recording control circuit 21 controls theinterface 12, the access control circuit 19, and the system controlcircuit 22 to record data.

When recording begins, the signal synchronizing circuit 42 switches theoperational clock output of the system clock generation circuit 41 tothe reference clock. As a result, the circuits 7–10, 12–16, 19–22 of theCD-R drive 1 are synchronized with the operational clock, or thereference clock.

The data provided from the personal computer 31 is stored in the buffermemory via the interface 12 and read from the buffer memory 13 in sectorunits. The encoder 14 encodes the data read from the buffer memory 13 insector units to generate recording data. The laser drive circuit 16provides the optical head 4 with drive signal having a voltagecorresponding to the recording data. In accordance with the drivesignal, the optical head 4 changes the intensity of the laser beamirradiated against the optical disc 32. This forms recording pits on therecording layer of the optical disc 32 and records data on the opticaldisc 32. Simultaneously, from the laser beam reflected by the opticaldisc 32, the optical head 4 reproduces the data recorded on the opticaldisc 32 as the RF signal. The RF amplifier 5 amplifies the RF signalprovided from the optical head 4 to generate digital data. The wobbledecoder 9 extracts the wobble component from the digital data and usesthe wobble component to generate the rotation control signal. Inaccordance with the rotation control signal, the spindle servo circuit 3controls the spindle motor 2 so that the optical disc 32 is rotated at aconstant linear velocity. The ATIP decoding circuit 10 decodes the ATIPusing the wobble component and extracts the ATIP address of the absolutetime information in the ATIP.

When the transmission rate of the data provided from the personalcomputer 31 is slower than the transmission rate of the data recorded inthe optical disc 32 (write speed), that is, when the transmission rateof the data provided to the buffer 13 is slower than that of the dataoutput from the encoder 14, the amount of data stored in the buffermemory 13 decreases. When the buffer underrun determination circuit 20determines that a buffer underrun error may occur in the buffer memory13, the recording control circuit 21 controls the interrupt/restartcircuit 43 so that, before the occurrence of a buffer underrun in thebuffer memory 13, the address memories 47, 48 are accordingly providedwith the interrupt signal and the output of recording data from theencoder 14 is interrupted.

In this state, when the level of the recording data output from theencoder 14 goes low, the interrupt/restart circuit 43 outputs theinterrupt signal and stops the output of the recording data from theencoder 14. In response to the interrupt signal, the address memories47, 48 store the data address of the buffer memory 13. In other words,the address memory 47 stores the buffer memory address of the data readfrom the buffer memory 13 when receiving the interrupt signal. Theaddress memory 48 stores the ATIP address of the ATIP decoding circuit10 when receiving the interrupt signal.

When the output of the recording data from the encoder 14 isinterrupted, the transmission of the drive signal from the laser drivecircuit 16 to the optical head 4 is impeded. This stops the emission ofthe laser beam from the optical head 4 and interrupts the recording ofdata on the optical disc 32.

When the interrupt/restart circuit 43 outputs the interrupt signal, thesector of the data being output from the encoder 14 is recorded on theoptical disc 32. The interrupt signal of the interrupt/restart circuit43 may be output at times between sectors of the recording data.

Subsequent to the recording interruption, the data provided from thepersonal computer 31 is stored in the buffer memory 13 via the interface12. As the amount of data stored in the buffer memory 13 increases, thestate in which a buffer underrun may occur no longer exists. When thebuffer underrun determination circuit 20 determines that buffer underrunis not likely to occur, the recording control circuit 21 controls theaccess control circuit 19 and the system control circuit 22 to performdata reproduction in the recording restart mode.

When data reproduction is performed in the recording restart mode, theaccess control circuit 19 controls the head servo circuit 6. The headservo circuit 6 controls focusing, tracking, and sled feed of theoptical head 4 to move the optical head 4 to a sector location that isprior by a predetermined number of sectors from the sector at which therecording interruption occurred. The optical head 4 then irradiates thelaser beam from that sector location.

The interrupt/restart circuit 43 controls the laser drive circuit 16 sothat a drive signal having a constant voltage is output from the laserdrive circuit 16. This results in the optical head 4 irradiating theoptical disc 32 with a relatively weak laser beam. The reflected laserbeam reproduces the data recorded on the optical disc prior to therecording interruption, and the optical head 4 outputs the RF signal.The RF signal is amplified by the RF amplifier 5 and converted todigital data. The decoder 7 decodes the digital data, extracts a pitclock from the digital data, and separates a subcode from the digitaldata. A subcode synchronizing signal is generated from the subcode. Thesubcode is decoded by the subcode decoding circuit 8 to generate thesub-Q data.

When data reproduction in the recording restart mode is started, thesignal synchronizing circuit 42 switches the operational clock from thereference clock of the crystal oscillation circuit 18 to thereproduction clock of the decoder 7. The circuits 7–10, 12–16, 19–22 ofthe CD-R drive 1 are operated in accordance with the reproduction clock.By using the reproduction clock, the data recorded on the optical disc32 prior to the recording interruption is accurately reproduced.

The recording control circuit 21 controls the interrupt/restart circuit43 to instruct the encoder 14 to restart the output of the recordingdata. The encoder 14 goes back by a predetermined number of sectors fromthe data address of the buffer memory 13 at which the recordinginterruption occurred and starts reading data in sector units from thatsector of the buffer memory 13. The encoder 14 adds a synch byte, aheader, an EDC, and an ECC to the read data, performs the CIRC and EFMprocesses, and adds a subcode, which includes the sub-Q data, and thesubcode synchronizing signal to the read data.

The drive signal of the laser drive circuit 16 is constant during datareproduction in the recording restart mode. In other words, the drivesignal of the laser drive circuit 16 has a low voltage. Accordingly,laser irradiation does not affect the data recorded on the optical discprior to the interruption.

The signal synchronizing circuit 42 controls the access control circuit19 via the recording control circuit 21 and synchronizes the datarecorded on the optical disc 32 with the recording data output from theencoder 14. In other words, the signal synchronizing circuit 42 controlsthe recording control circuit 21 and the access control circuit 19 sothat the subcode synchronizing signal of the decoder 7 is synchronizedwith the subcode synchronizing signal of the encoder 14 and the sub-Qdata of the subcode decoding circuit 8 is associated with the sub-Q dataof the encoder 14.

The location detection circuit 45 compares the address of the data readfrom the buffer memory 13 with the address stored in the address memory47 and activates the restart signal when the data address and the storedaddress are the same. The address stored in the address memory 47 is theaddress of the data read from the buffer memory 13 when the recording ofdata is interrupted.

The location detection circuit 46 compares the ATIP address of the ATIPdecoding circuit 10 with the ATIP address stored in the address memory48 and activates the restart signal when the ATIP address and the storedaddress are the same. The ATIP address stored in the address memory 48is the ATIP address decoded by the ATIP decoding circuit 10 when therecording of data is interrupted.

When the restart signals of the location detection circuits 45, 46 aresimultaneously activated, the retry determination circuit controls theinterface 12, the access control circuit 19, and the system controlcircuit 22 via the recording control circuit 21. The signalsynchronizing circuit 42 switches the operational clock of the systemclock generation circuit 41 from the reproduction clock to the referenceclock when recording is restarted.

Upon the restart of the recording, the address of the data read from thebuffer memory 13 shifts to the address next to the address at which datarecording was interrupted. Further, the address memory 48 and thelocation detection circuit 46 shift the sector location of the opticaldisc 32 irradiated by the laser beam to the sector location next to thesector location at which data recording was interrupted. In this state,the signal synchronizing circuit 42 synchronizes the recording dataoutput from the encoder 14 with the data recorded on the optical disc32. Accordingly, the data of the sector next to the sector at which datarecording was interrupted is recorded upon the restart of the recording.In other words, sectors of data are recorded without any interruptionswhen restarting recording. This ensures the continuity of the recordeddata while preventing the occurrence of a buffer underrun error.

As described above, when the level of the recording data output from theencoder 14 goes low, the interrupt/restart circuit 43 outputs theinterrupt signal and stops the output of the recording data from theencoder 14. Thus, when the recording operation is restarted, therecording data output from the encoder 14 is low, and the laser drivecircuit 16 outputs a drive signal, the level of which is the same asthat when data is reproduced. Accordingly, the power of the laser beamemitted from the optical head 4 is relatively low. That is, the laserbeam power of the optical head 4 is low when restarting the recordingoperation at the same data recording location. Therefore, data that hasalready been recorded is not damaged even if the recording restartlocation is offset from where it should be. Further, since the laserbeam is not emitted against the recording section corresponding to thelow level data, the diameters of pits do not become non-uniform.

For example, if the high level of the recording data were output fromthe encoder 14, the drive signal output by the laser drive circuit 16would have a voltage level that is several tens of times greater thanwhen data is reproduced. Thus, the power of the laser beam output fromthe optical head 4 would be several tens of times greater than thatduring the data reproduction operation. However, it is difficult toinstantaneously activate the laser power of the optical head 4 toseveral tens of times greater than that during the data reproduction. Todo so, a certain time period would be necessary. Thus, it would taketime to increase the laser power to a desired level when activating theoptical head 4 simultaneously with restarting the recording operation.Such delay would form a non-recording section on the optical disc 32 andproduce an interruption in the recording data.

Further, when restarting the recording operation, if the optical head 4emits the laser beam against the wrong data sector of the optical disc32, data may rewritten to a sector on which data has already beenrecorded. In such case, if a high power laser beam is emitted against arecording layer of the optical head 32 at which recording pits havealready been formed, the recording pits may be enlarged and may overlapwith recording pits of other sectors or tracks. Consequently, data wouldnot be recorded correctly. Further, if the timing of the recordingrestart is delayed, data is not recorded at the recording restartposition. This may divide a pit into two and record erroneous data. Evenif the location where the recording is restarted exactly matches thelocation where the interruption occurred, the power of the laser beamprior to the interruption differs slightly from that subsequent to therestart. This would cause the recording pits at the recording restartposition to have non-uniform sizes that result in data read errors.

In the preferred embodiment, the recording operation is interrupted at atime at which the level of the recording data output from the encoder 14goes low. Thus, the power of the laser beam output from the optical head4 is low when the recording operation is restarted. As a result, theabove-described problems do not occur.

The optimal time for interrupting the writing of data is at the outputof synch pattern data allocated to the head of each sector. In the CDstandards, a synch pattern has 24 bits and includes 11 high bits and 11low bits. In other words, the head of each sector includes a period of11 consecutive low bits, which is the longest low period in the CDstandards. An address is designated for each sector. Thus, the addressmemories 47, 48 hold address data corresponding to sector addresses.Accordingly, the optimal time for interrupting data writing would beduring the synch pattern of a sector. By interrupting the writing ofdata in this manner, it is not necessary to activate the laser power ofthe optical head 4 when restarting the recording operation and theformation of abnormal recording pits due to the rewriting of recordingdata is prevented.

It is preferred that the buffer underrun determination circuit 20determine that there is a possibility of a buffer underrun occurringwhen at least one sector of data is still in the buffer memory 13.

When the two restart signals of the location detection circuits 45, 46are not synchronously activated (when the two restart signals areactivated at different times), the retry determination circuit 44repeatedly perform data reproduction in the recording restart mode untilthe two restart signals are synchronously activated. In other words, ifan external disturbance occurs for one reason or another (e.g., theapplication of an external impact to the CD-R drive), the elements 2–22of the CD-R drive 1 may function erroneously such that the two restartsignals are not synchronously activated. Thus, the retry determinationcircuit 44 repeats data reproduction to avoid the influence of anexternal disturbance. If the restart signals of the position detectioncircuits 45, 46 are simultaneously activated, the retry determinationcircuit 44, the position detection circuit 45, and the address memory 47may be deleted.

FIG. 2( a) is a schematic view showing a sector of the optical disc 32.FIG. 2( b) is a diagram illustrating the addresses of the buffer memory13. Sectors Sn+1, Sn, Sn−1, Sn−2, . . . , Sn−m shown in FIG. 2( a) arerespectively associated with addresses An+1, An, An−1, An−2, . . . ,An−m shown in FIG. 2( b).

During recording, data is read from the buffer memory 13 in the order ofaddresses An−m, . . . , An−2, An−1, An, and the recording data encodedby the encoder 14 is recorded on the optical disc 32 in the order ofsectors Sn−m, . . . , Sn−2, Sn−1, Sn. For example, if the bufferunderrun determination circuit 20 determines during the recording ofdata that a bus underrun may occur at address An, the data of sector Sn,which is associated with address An, is recorded. However, the recordingof data is interrupted from the sector Sn+1, which is associated withaddress An+1.

When the recording of data is interrupted, address An is stored in theaddress memory 47, and the address of the ATIP decoded from the datarecorded at sector Sn is stored in the address memory 48. Afterward,when the buffer underrun determination circuit 20 determines that abuffer underrun is no longer likely to occur, data reproduction in therecording restart mode is commenced from sector Sn−m by going back fromsector Sn, at which recording was interrupted, by a predetermined numberof sectors (in this case, m sectors).

When data reproduction is commenced, data is read from the buffer memory13 from address An−m by going back from address An, at which recordingwas interrupted, by a predetermined number of addresses (m addresses).The read data is encoded into recording data by the encoder 14.

The signal synchronizing circuit 42 synchronizes the recording dataoutput from the encoder 14 with the data recorded on the sectors Sn−m toSn of the optical disc 32. Then, when the address of the data read fromthe buffer memory 13 matches the address An stored in the address memory47, the restart signal of the location detection circuit 45 isactivated. When the address of the ATIP decoded by the ATIP decodingcircuit 10 matches the ATIP address of the sector Sn stored in theaddress memory 48, the restart signal of the location detection circuit46 is activated. When the two restart signals of the location detectioncircuits 45, 46 are simultaneously activated, the retry determinationcircuit 44 restarts the recording of data from sector Sn+1, which isnext to the sector Sn at which data recording was interrupted.

It is preferred that the predetermined sector number (m sectors) besufficient for obtaining time period T1, which is required for thespindle serve circuit 3 to control the spindle motor 2 and the headservo circuit 6 to control the optical head 4, and time period T2, whichis required for synchronization by the signal synchronizing circuit 42.For example, m is set at 10 to 30. The time periods T1, T2 increase asthe recording speed of the CD-R drive 1 becomes higher, for example, asthe recording speed increases from 4× to 8×. Accordingly, it ispreferred that the predetermined sector number be increased as therecording speed increases.

In the present invention, the recording operation is interrupted whenthe power level of the laser beam becomes low or during the period whenthe power of the emitted laser beam is low. This prevents the formationof non-uniform recording pits at the recording restart location. Thus,abnormal recording pits are not formed due to the rewriting of data.

The recording operation is interrupted when the power level of the laserbeam is low and the synch pattern data of the 11 consecutive, low levelbits is output. Further, the address of the sector at which therecording interruption occurred is stored in the address memories.Accordingly, the synch pattern and the sector address facilitates therestart of data recording.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. Particularly, it should beunderstood that the present invention may be embodied in the followingforms.

(1) The present invention may be applied to a data recorder employingthe constant angular velocity (CAV) method. In such case, a clocksynchronized with the wobble component, which is extracted by the wobbledecoder 9, is generated and used as the operational clock during therecording of data.

(2) The access control circuit 19, the buffer underrun determinationcircuit 20, the recording control circuit 21, and the system controlcircuit 22 may be replaced by a microcomputer that includes a CPU, aROM, and a RAM. In other words, the function of each circuit may beachieved by having a microcomputer perform various operations.

(3) The present invention may be applied to a data recorder (e.g., CD-RWdrive, MD drive) that uses a rewritable recording medium (e.g., CD-RWstandard optical disc, MD standard optical disc). In such case, theoccurrence of a buffer underrun error is prevented. This decreases thetime required for the recording of data.

The present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. A data recorder for recording data on a recording medium by emitting a laser beam against the recording medium, the data recorder comprising: a laser drive circuit, which controls the power level of the laser beam, wherein the laser beam is generated at a relatively high power level sufficient to form a recording pit on a recording layer of the recording medium and at a relatively low power level insufficient to form a recording pit on the recording layer of the recording medium in accordance with the recording data; and an interrupt control circuit for interrupting data recording when a predetermined state in which buffer underrun may occur is detected, wherein the interruption occurs when the laser beam is generated at a relatively low power level.
 2. The data recorder according to claim 1, wherein the recording data includes synch pattern data, the power level of the laser beam corresponding to the synch pattern data is the relatively low power level and the relatively high power level, and the interrupt control circuit interrupts data recording when the laser beam is generated at the relatively low power level in accordance with the synch pattern data.
 3. A data recorder for recording data on a recording medium by emitting a laser beam against the recording medium, the data recorder comprising: a buffer memory for temporarily storing data that is to be recorded on the recording medium; an interrupt control circuit for interrupting data recording when a predetermined state in which buffer underrun may occur is detected; an address memory connected to the buffer memory, wherein the address memory stores at least one of an address of the recording medium and an address of the buffer memory when data recording on the recording medium is interrupted, each address indicating a location of data when the recording interruption occurred; a synchronizing circuit for sequentially reading the data recorded on the recording medium prior to the recording interruption and the data stored in the buffer memory prior to the recording interruption and synchronizing the recorded data and the stored data; and a restart circuit for restarting data recording on the recording medium based on the address stored in the address memory, wherein the interrupt control circuit interrupts data recording when the laser beam is generated at a relatively low power level.
 4. The data recorder according to claim 3, wherein the data includes synch pattern data, the power level of the laser beam corresponding to the synch pattern data is the relatively low power level and the relatively high power level, and the interrupt control circuit interrupts data recording when the laser beam is generated at the relatively low power level in accordance with the synch pattern data.
 5. The data recorder according to claim 4, wherein the data is recorded in the recording medium in sector units, each sector including sector address data, and wherein the address memory stores the sector address data where the recording interruption occurred.
 6. The data recorder according to claim 5, wherein the predetermined state is a state in which there is a possibility that the amount of data in the buffer memory may become null and cause the buffer memory to become empty.
 7. A data recorder for recording data on a recording medium, the recorder comprising: a buffer memory for temporarily storing data; an encoder connected to the buffer memory to encode the data read from the buffer memory and to generate recording data; a recording unit connected to the encoder to emit a laser beam against the recording medium in accordance with the recording data and record the recording data on the recording medium; and an interrupt control circuit connected to the encoder to detect a predetermined state in which buffer underrun may occur during data recording, wherein, upon the detection of the predetermined state, the interrupt control circuit controls the encoder so that data recording is interrupted when the laser beam is generated at a relatively low power level.
 8. The data recorder according to claim 7, wherein the data includes synch pattern data, and the interrupt control circuit interrupts data recording when the laser beam is generated at the low power level in accordance with the synch pattern data.
 9. The data recorder according to claim 8, wherein the predetermined state is a state in which there is a possibility that the amount of data in the buffer memory may become null and cause the buffer memory to become empty.
 10. A method for recording data on a recording medium by emitting a laser beam against the recording medium, the method comprising: temporarily storing data in a buffer memory; recording data read from the buffer memory on the recording medium; interrupting data recording when a predetermined state in which buffer underrun may occur is detected; storing in an address memory at least one of an address of the recording medium and an address of the buffer memory when data recording on the recording medium is interrupted, each address indicating a location of data when the recording interruption occurred; sequentially reading the data recorded on the recording medium prior to the recording interruption and the data stored in the buffer memory prior to the recording interruption; synchronizing the recorded data and the stored data; and restarting data recording on the recording medium based on the address stored in the address memory, wherein the interrupting of the data recording is performed when the laser beam is generated at a relatively low power level. 